I had a 65 Tempest with a 326 and powerglide. All I did was find a short shaft T400 and bolt it in. The driveshaft yoke need changed to the bigger one, but the length was the same. The shifter was on the column and it even worked. When in low gear, the indicator rear below the 1 mark and just above it when in 2nd gear. 3rd read right on. You shouldn't have any trouble at all.
You do know the T350's have a cable for the down shift that is operated off the throttle lever. I am running one behind a 250 now, and never hooked up the cable. I just plugged the hole. If I want to down shift, I just pull it down. Seems to work just fine. I may add it later If I find the right brackets in the salvage yard some day. Joe